have shown they could challenge for a major, including Japan's Kei Nishikori and Milos Raonic of Canada.
With Rafael Nadal returning from an appendix operation, Roger Federer now 33 and Andy Murray struggling for form, Cilic expects an even more open season next year.
World No 1 Novak Djokovic from Serbia is the last of the 'Big Four'.
"Rafa is a little bit injured, he's going to be also back hopefully for the start of the new season, so that's (recovery) going to make it even more competitive.
"I think next year we might see another new Grand Slam winner."
Cilic said Stanislas Wawrinka's Australian Open win in January opened the door to a breakthrough year for several players, culminating in his (Cilic's) US Open final against Nishikori in September.
"This year Nishikori played amazing, (Grigor) Dimitrov played also a really good season Zapatillas Vans Old Skool Pro Negras Baratas , Raonic was there all the time so it gives openings for those players to be there more often and being used to being at the end of the tournament," Cilic said.
France's Gael Monfils was also hopeful about a Grand Slam breakthrough after completing his season with a victory over Federer in the Davis Cup final.
"The tour has changed a little bit and the top players also have changed a little bit," Monfils said.
"Everyone improved a lot and, as Marin said, guys like him and Wawrinka won a Grand Slam where before it was only the 'Big Four' Zapatillas Vans Old Skool Rebajas Negras Grises , as you guys call them.
"Definitely I hope next year I can be part of the new crop."
Cilic, 26, said he hoped that playing the IPTL, instead of his usual routine of focusing solely on fitness work at this time, would prove good preparation for the Australian Open.